Helmet sizes are generally known to include four types, i.e., S size (55 cm to 56 cm), M size (57 cm to 58 cm), L size (59 cm to 60 cm) and XL size (61 cm or more). Each of the above values indicates the circumferential length of the head of a helmet wearer. In helmets of the four types of sizes, portions corresponding to the head circumferential lengths of the head accommodating spaces are substantially similar ellipses.
When a helmet shop selling helmets is to sell a helmet to a prospective helmet purchaser such as a prospective helmet wearer who is to wear a helmet, in one case, the shop sells a helmet of the size that the prospective helmet purchaser indicates. In another case, the employee of the helmet shop measures the circumferential length of the head of the prospective helmet wearer with a tape measure or the like. The employee selects the type of the matched size from the matched sizes indicated on the tape measure or the like, and sells a helmet of the selected type to the prospective helmet purchaser.
There has been conventionally known use of a personal computer using software (i.e., a computer program) for elliptic shape calculation in the helmet shop. In this case, the employee of the helmet shop measures the back-and-forth length and left-and-right width of the head of the prospective helmet wearer using a measure such as a head size measuring tool, a rule, or the like. The circumferential length of the head is calculated from the measurement values using the personal computer. The type of the recommendable helmet size is selected on the basis of the calculated value from the sizes attached to the helmets of the respective types of sizes.
The above conventional method, however, has the following drawbacks. More specifically, both measurement of the circumferential length of the head using the tape measure and calculation of the circumferential length of the head using the elliptic shape calculation program are based on the assumption that the head of the prospective helmet wearer has a specific elliptic shape substantially similar to the elliptic shape of an average human head. Hence, the ratio of the major axis to the minor axis of the specific elliptic shape is substantially constant regardless of the type of the helmet size.
The perimetric shape of the head of the prospective helmet wearer differs from one person to another even if the circumferential length is the same, and does not always substantially coincide with the specific elliptic shape. Therefore, when selecting the type of the helmet size on the basis of only the circumferential length of the head of the prospective helmet wearer, the helmet having the size of the selected type may not fit (that is, match) the head of the prospective helmet wearer. In this case, the prospective helmet wearer must wear a helmet having a size larger than necessary.
For example, according to Japanese Patent Laid-Open No. 2000-160424, to eliminate the drawbacks in the conventional method as described above, a pocket is formed in the neck pad, and a plate-like adjusting pad is inserted in the pocket, thereby adjusting the size of the helmet. In this case, although the size of the helmet can be decreased, it cannot be increased. As the plate-like adjusting pad is inserted in the pocket, not only the operation of inserting and removing the adjusting pad into and from the pocket is cumbersome, but also the inner surface of the helmet becomes coarse. This makes the helmet wearer feel uneasy when wearing the helmet, giving an uncomfortable set. To eliminate this coarseness, the outer portion of the adjusting pad may be tapered to be gradually thin toward the outer side. In this case, however, the operation of inserting and removing the adjusting pad into and from the pocket becomes more cumbersome, and the adjusting pad tends to be damaged and broken easily.